New York: People who have had a kidney stone seem to have a heightened risk of gallstones -- and vice versa, according to a new study.

Researchers already know that obesity, diabetes and having a generally unhealthy diet put people at risk for both types of stones. But even when those common risks were taken into account, the link remained.

The report "raises our antenna to this shared relationship between these two disorders," said Dr. Brian Matlaga, a urologist at the Johns Hopkins University School of Medicine in Baltimore.

"From an anecdotal standpoint, certainly it`s not an uncommon scenario that a patient would have had both," Matlaga, who wasn`t involved in the new research, told Reuters Health. But, he continued, "I`m a little bit at a loss trying to define what that relationship would be."

That`s because stones in the kidney and gallbladder form differently, he said, and are made of two different things -- kidney stones of calcium and gallstones of cholesterol, most of the time.

Data for the current analysis came from three different long-term studies of nurses and doctors who completed a health and lifestyle questionnaire, then reported any new medical conditions every two years afterward. In total, more than 240,000 people were followed for between 14 and 24 years.

Over that time, there were about 5,100 new kidney stones diagnosed and close to 18,500 new cases of gallstones.

Depending on the population -- male or female, older or younger -- people with a history of gallstones were between 26 and 32 percent more likely to get a kidney stone than people who hadn`t ever had gallstones.

And the link also went in the opposite direction. A past history of kidney stones meant study participants were between 17 and 51 percent more likely to report a new gallstone.

That was after factoring in the impact of age, diabetes, high blood pressure, weight and certain aspects of diet on the risk of both kinds of stones.

Researchers led by Eric Taylor from the Maine Medical Center in Portland said it`s possible that a shift in the type of bacteria in the intestines might somehow predispose people to both kidney stones and gallstones. But, Taylor said, "the fairest thing is that we just don`t know" why the two would be linked.

In their report in the Journal of Urology the researchers echoed Matlaga`s call for more detailed research into any explanations for a common cause -- which might help doctors prevent or treat both kidney stones and gallstones, they added.

"They are really two different kinds of stones, so the relationship is not going to be simple between the two conditions," Taylor said.

Matlaga said that for now, there are steps people can take to reduce their risk of both gallstones and kidney stones, even if they`ve already had one condition.

"You`d like to try to minimize those common risk factors and work on things like weight loss and cholesterol control," he said.

Taylor agreed that the findings "emphasize the importance of healthy diet and healthy weight."